1. Technical Field
The invention is related to producing a High Dynamic Range (HDR) image from a series of bracketed images, and more particularly to a system and process for generating such HDR images, even in the presence of scene or camera motion between the images.
2. Background Art
The real world has a lot more brightness variation than can be captured by the sensors available in most cameras today. The radiance of a single scene may contain four orders of magnitude in brightness—from shadows to fully lit regions. Typical CCD or CMOS sensors only capture about 256–1024 brightness levels.
This limited dynamic range problem has inspired many solutions in recent years. One method of capturing the full radiance of a static scene is to take multiple exposures of the scene and then to combine them to create a High Dynamic Range (HDR) map [3, 7, 8, 9,12]. Because these technologies require multiple input images, there is a potential for motion between the inputs due to either dynamic elements in the scene or a moving (e.g., handheld) camera. Mitsunaga et al. [9] adddress this problem to a limited extent by fitting a global motion model to the inputs. Mann et al. [8] register differently exposed frames using homographies, which can compensate for larger camera rotations. Bogoni [2] uses affine motion followed by per-pixel flow to register different exposures, but details of the frame registration are not given.
The need to fuse images taken at different times can be eliminated (and thus eliminate the motion problem) using multiple image detectors, novel sensors or spatially varying pixel exposures [10]. However, the focus of the present invention is on what can be achieved using widely available conventional (i.e., low dynamic range) image sensors and cameras.
Once an HDR image is computed, it can then be rendered to a display. Since typical displays are only able to yield about two orders of magnitude in brightness values, a contrast reduction must be performed on the HDR image. This so-called tone mapping problem has recently been explored by a number of researchers [4, 5, 11].
It is noted that in the preceding paragraphs, as well as in the remainder of this specification, the description refers to various individual publications identified by a numeric designator contained within a pair of brackets. For example, such a reference may be identified by reciting, “reference [1]” or simply “[1]”. Multiple references will be identified by a pair of brackets containing more than one designator, for example, [2, 3]. A listing of references including the publications corresponding to each designator can be found at the end of the Detailed Description section.